1. Field
The present invention relates generally to communications, and more specifically, to improving the reliable conveyance of orthogonal space information used to identify code channels in a spread spectrum communication system.
2. Background
The field of wireless communications has many applications including, e.g., cordless telephones, paging, wireless local loops, personal digital assistants (PDAs), Internet telephony, and satellite communication systems. A particularly important application is cellular telephone systems for mobile subscribers. As used herein, the term “cellular” system encompasses systems operating on both cellular and personal communication services (PCS) frequencies. Various over-the-air interfaces have been developed for such cellular telephone systems including, e.g., frequency division multiple access (FDMA), time division multiple access (TDMA), and code division multiple access (CDMA). In connection therewith, various domestic and international standards have been established including, e.g., Advanced Mobile Phone Service (AMPS), Global System for Mobile (GSM), and Interim Standard 95 (IS-95). IS-95 and its derivatives, IS-95A, IS-95B, ANSI J-STD-008 (often referred to collectively herein as IS-95), and proposed high-data-rate systems are promulgated by the Telecommunication Industry Association (TIA) and other well known standards bodies.
Cellular telephone systems configured in accordance with the use of the IS-95 standard employ CDMA signal processing techniques to provide highly efficient and robust cellular telephone service. Exemplary cellular telephone systems configured substantially in accordance with the use of the IS-95 standard are described in U.S. Pat. Nos. 5,103,459 and 4,901,307, which are assigned to the assignee of the present invention and incorporated by reference herein. An exemplary system utilizing CDMA techniques is the cdma2000 ITU-R Radio Transmission Technology (RTT) Candidate Submission (referred to herein as cdma2000), issued by the TIA. The standard for cdma2000 is given in the draft versions of IS-2000 and has been approved by the TIA and 3GPP2. Another CDMA standard is the W-CDMA standard, as embodied in 3rd Generation Partnership Project “3GPP”, Document Nos. 3G TS 25.211, 3G TS 25.212, 3G TS 25.213, and 3G TS 25.214.
The telecommunication standards cited above are examples of only some of the various communication systems that can be implemented. Some of these various communication systems are configured so that remote stations can transmit information regarding the quality of the transmission medium to a serving base station. As described herein, a “serving” base station is a base station in communication with the remote station. This channel information can then be used by the serving base station to optimize the power levels, the transmission formats, and the timing of forward link transmissions, and further, to control the power levels of reverse link transmissions.
As used herein, “forward link” refers to all transmissions directed from a base station to a remote station and “reverse link” refers to all transmissions directed from a remote station to a base station. The forward link and the reverse link are uncorrelated, meaning that observations of one do not facilitate the prediction of the other. However, for stationary and slow-moving remote stations, the characteristics of the forward link transmission path will be observed to be similar to the characteristics of the reverse link transmission path in a statistical sense.
The forward link is a shared resource between remote stations. To ensure simultaneous transmissions to a plurality of remote stations, channelization using orthogonal codes can be implemented. The number of orthogonal codes is a limited system resource and must be allocated and re-allocated on a dynamic basis. The choice of which orthogonal code to use is part of the optimization process implemented by the base station.
Transmissions for a particular remote station are sent on a dedicated channel and transmissions for a group of remote stations are sent in a broadcast manner. The transmissions on the dedicated channel are encoded using a set of parameters that are picked from a large selection of potential parameters. If the remote station does not know the particular set of parameters that were used by a base station, then the remote station would have to attempt to demodulate and decode the transmission using every set of parameters, until the transmission is decoded correctly. This is an inefficient methodology. Hence, transmission format information is typically transmitted on a broadcast channel so that a remote station could receive the transmission format information. The remote stations are configured to use assigned transmission format information in order to decode the broadcast channel.
For example, if data is to be sent to a remote station, the base station would package the data according to a given transmission format, i.e., “packaging,” and send both the packaged data and information about the type of packaging used to the remote station. Knowledge as to the type of packaging allows the remote station to open the packaged data quickly and efficiently. However, sending the packaging information can be problematic.
In order to improve the data throughput rates, transmission format information must be sent in a manner that is easily demodulated and decoded by the remote station. Typically, the transmission format information is sent as a broadcast, so that the remote station can demodulate and decode the information quickly, without set-up delays. However, there are flaws that are common and inevitable to all broadcast transmissions: reliability and efficiency. For a broadcast transmission, the base station cannot readily determine who may have received the broadcast and who may have missed the broadcast. Hence, if broadcasted transmission format information is missed, a remote station may also miss the corresponding transmission on the dedicated channel.